It could be some sort of diesel-electric drivetrain like most locomotives. The fuel efficiency and power in diesel-electric locomotives has been proven for decades.
But the article is not clear on that.
DOD has been developing solid oxide fuel cell technology that runs on JP-8 since 2010 or earlier. The stated purpose has always been low maintenance, high efficiency gensets, but I recall some talk about testing it in APCs and such for electric drive power. The big problem then was dealing with the fuel cell's waste heat, not insignificant on the battlefield.
No telling what's under the hood now (or what might be slated for later production).
The fuel efficiency and power in diesel-electric locomotives has been proven for decades.
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Especially when those diesel-electric locomotives where sent into combat under adverse conditions and hostile fire.